1. Field of the Invention
The present invention relates to a differential gear unit for motor vehicles, and more particularly to a differential gear unit provided with a limited slip mechanism for restricting the differential function of the gear unit when a difference in rotational speed between side shafts exceeds a predetermined value.
2. Description of the Prior Art
In Japanese Patent Publication No. 56-21942, there has been proposed a differential gear unit provided with such a limited slip mechanism as described above which comprises a first cam element integral with one side gear of the gear unit, a second cam element axially slidably and rotatably mounted on a hub portion of the side gear and being engaged with the first cam element to be axially displaced by its cam action when rotated relatively to the first cam element, a friction clutch assembly including a first set of cluth discs axially slidably mounted on the hub portion of the side gear for rotation therewith and a second set of clutch discs axially slidably carried by the differential case for rotation therewith and being interposed between the first set of clutch discs for frictional engagement therewith, and means for effecting relative rotation between the cam elements when a difference in rotational speed between side shafts excees a predetermined value.
In operation of the limited slip mechanism, axial displacement of the second cam element is caused by relative rotation between the cam elements, and in turn the first set of clutch discs are brought into frictional engagement with the second set of clutch discs in response to the axial displacement of the second caam element to restrict the differential function of the gear unit. When the differential function of the gear unit is instantly restricted in response to relative rotation between the cam elements, unpleasasnt shocks will occur during travel of the vehicle. If the left and right road wheels alternately spin during travel of the vehicle on a desert road, the differential gear unit will be frequently locked and released. If one of the road wheels spins during travel of the vehicle on a roaad of low frictional coefficient, the differential gear unit will be locked unexpectedly.